1. Field of the Invention
The present invention relates to an organic light emitting device, and more specifically to an organic light emitting device using a benzofluoranthene derivative.
2. Description of the Related Art
An organic light emitting device is a device in which a thin film including a fluorescent organic compound or a phosphorescent organic compound is sandwiched between an anode and a cathode. Further, electrons and holes are injected from the respective electrodes to generate exciton of the fluorescent compound, whereby the organic light emitting device emits light when the exciton returns to a ground state.
According to a study at Eastman Kodak company in 1987 (Appl. Phys. Lett. 51, 913 (1987)), there is reported a device having a function-separation type two-layer structure. Specifically, there is reported a device using ITO as an anode, a magnesium-silver alloy as a cathode, an aluminum quinolinol complex as an electron transporting material and a light emitting material, and a triphenylamine derivative as a hole transporting material. In the device having the function-separation type two-layer structure, there is reported a light emission of approximately 1,000 cd/m2 at an applied voltage of approximately 10 V.
Recent progress of an organic light emitting device is remarkable, and the characteristics of the device enable a light emitting device with a high luminance at a low applied voltage, a variety of emission wavelengths, high-speed responsiveness, thin and light weight. From this fact, it is suggested that the organic light emitting device have potential to find use in a wide variety of applications. The organic light emitting device still involves many problems in terms of durability such as a change with time due to long-term use and deterioration due to, for example, an atmospheric gas containing oxygen or humidity. Further, when it is attempted that the device is applied to a full-color display, at present, blue light, green light, and red light each having a longer life, high conversion efficiency, and high color purity need to emitted. Various proposals have been made so as to solve the problems.
Here, in order to solve the problems, a benzofluoranthene derivative has been proposed as a material for the organic light emitting device. Japanese Patent Application Laid-Open No. H10-189247, Japanese Patent Application Laid-Open No. 2005-68087, and Japanese Patent Application Laid-Open No. 2005-272805 report an organic light emitting device using a benzo(k)fluoranthene derivative. Moreover, US Patent Application Publication No. 2004-0076853 reports that an unsubstituted benzo(ghi)fluoranthene is not suitable as a light emitting material due to large intermolecular interaction and that an unsubstituted indeno chrysene is used as a second host material that is likely to form an aggregate. Moreover, US Patent Application Publication No. 2004-0076853 reports an example in which a benzo(ghi)fluoranthene, in which an unsubstituted benzene ring has been introduced to the 1st and 6th positions, has been used similarly as a second host material that is likely to form an aggregate.